A newly identified cluster of glutathione S-transferase genes provides Verticillium wilt resistance in cotton.

As the largest cultivated fiber crop in the world, cotton (Gossypium hirsutum) is often exposed to various biotic stresses during its growth periods. Verticillium wilt caused by Verticillium dahliae is a severe disease in cotton, and the molecular mechanism of cotton resistance for Verticillium wilt needs to be further investigated. Here, we revealed that the cotton genome contains nine types of GST genes. An evolutionary analysis showed that a newly identified cluster (including Gh_A09G1508, Gh_A09G1509 and Gh_A09G1510) located on chromosome 09 of the A-subgenome was under positive selection pressure during the formation of an allotetraploid. Transcriptome analysis showed that this cluster participates in Verticillium wilt resistance. Because the Gh_A09G1509 gene showed the greatest differential expression in the resistant cultivar under V. dahliae stress, we overexpressed this gene in tobacco and found that its overexpression resulted in enhanced Verticillium wilt resistance. Suppression of the gene cluster via virus-induced gene silencing made cotton plants of the resistant cultivar Nongda601 significantly susceptible. These results demonstrated that the GST cluster played an important role in Verticillium wilt resistance. Further investigation showed that the encoded enzymes of the cluster were essential for the delicate equilibrium between the production and scavenging of H2 O2 during V. dahliae stress.

Genome-wide identification of the expansin gene family reveals that expansin genes are involved in fibre cell growth in cotton.

BACKGROUND: Expansins (EXPs), a group of proteins that loosen plant cell walls and cellulosic materials, are involved in regulating cell growth and diverse developmental processes in plants. However, the biological functions of this gene family in cotton are still unknown. RESULTS: In this paper, we identified a total of 93 expansin genes in Gossypium hirsutum. These genes were classified into four subfamilies, including 67 GhEXPAs, 8 GhEXPBs, 6 GhEXLAs, and 12 GhEXLBs, and divided into 15 subgroups. The 93 expansin genes are distributed over 24 chromosomes, excluding Ghir_A02 and Ghir_D06. All GhEXP genes contain multiple exons, and each GhEXP protein has multiple conserved motifs. Transcript profiling and qPCR analysis revealed that the expansin genes have distinct expression patterns among different stages of cotton fibre development. Among them, 3 genes (GhEXPA4o, GhEXPA1A, and GhEXPA8h) were highly expressed in the initiation stage, 9 genes (GhEXPA4a, GhEXPA13a, GhEXPA4f, GhEXPA4q, GhEXPA8f, GhEXPA2, GhEXPA8g, GhEXPA8a, and GhEXPA4n) had high expression during the fast elongation stage, and GhEXLA1c and GhEXLA1f were preferentially expressed in the transition stage of fibre development. CONCLUSIONS: Our results provide a solid basis for further elucidation of the biological functions of expansin genes in relation to cotton fibre development and valuable genetic resources for future crop improvement.

Cotton S-adenosylmethionine decarboxylase-mediated spermine biosynthesis is required for salicylic acid- and leucine-correlated signaling in the defense response to Verticillium dahliae.

MAIN CONCLUSION: Cotton S-adenosylmethionine decarboxylase-, rather than spermine synthase-, mediated spermine biosynthesis is required for salicylic acid- and leucine-correlated signaling in the defense response to Verticillium dahliae. Spermine (Spm) signaling is correlated with plant resistance to the fungal pathogen Verticillium dahliae. We identified genes for key rate-limiting enzymes in the biosynthesis of Spm, namely S-adenosylmethionine decarboxylase (GhSAMDC) and Spm synthase (GhSPMS). These were found by screening suppression subtractive hybridization and cDNA libraries of cotton (Gossypium) species tolerant to Verticillium wilt. Both were induced early and strongly by inoculation with V. dahliae and application of plant hormones. Silencing of GhSPMS or GhSAMDC in cotton leaves led to a significant accumulation of upstream substrates and, ultimately, enhanced plant susceptibility to Verticillium infection. Exogenous supplementation of Spm to the silenced cotton plants improved resistance. When compared with the wild type (WT), constitutive expression of GhSAMDC in Arabidopsis thaliana was associated with greater Verticillium wilt resistance and higher accumulations of Spm, salicylic acid, and leucine during the infection period. By contrast, transgenic Arabidopsis plants that over-expressed GhSPMS were unexpectedly more susceptible than the WT to V. dahliae and they also had impaired levels of putrescine (Put) and salicylic acid (SA). The susceptibility exhibited in GhSPMS-overexpressing Arabidopsis plants was partially reversed by the exogenous supply of Put or SA. In addition, the responsiveness of those two transgenic Arabidopsis lines to V. dahliae was associated with an alteration in transcripts of genes involved in plant resistance to epidermal penetrations and amino acid signaling. Together, these results suggest that GhSAMDC-, rather than GhSPMS-, mediated spermine biosynthesis contributes to plant resistance against V. dahliae through SA- and leucine-correlated signaling.

Transcriptome profiling of Gossypium barbadense inoculated with Verticillium dahliae provides a resource for cotton improvement.

BACKGROUND: Verticillium wilt, caused by the fungal pathogen Verticillium dahliae, is the most severe disease in cotton (Gossypium spp.), causing great lint losses worldwide. Disease management could be achieved in the field if genetically improved, resistant plants were used. However, the interaction between V. dahliae and cotton is a complicated process, and its molecular mechanism remains obscure. To understand better the defense response to this pathogen as a means for obtaining more tolerant cultivars, we monitored the transcriptome profiles of roots from resistant plants of G. barbadense cv. Pima90-53 that were challenged with V. dahliae. RESULTS: In all, 46,192 high-quality expressed sequence tags (ESTs) were generated from a full-length cDNA library of G. barbadense. They were clustered and assembled into 23126 unigenes that comprised 2661 contigs and 20465 singletons. Those unigenes were assigned Gene Ontology terms and mapped to 289 KEGG pathways. A total of 3027 unigenes were found to be homologous to known defense-related genes in other plants. They were assigned to the functional classification of plant-pathogen interactions, including disease defenses and signal transduction. The branch of "SA→NPR1→TGA→PR-1→Disease resistance" was first discovered in the interaction of cotton-V. dahliae, indicating that this wilt process includes both biotrophic and necrotrophic stages. In all, 4936 genes coding for putative transcription factors (TF) were identified in our library. The most abundant TF family was the NAC group (527), followed by G2-like (440), MYB (372), BHLH (331), bZIP (271) ERF, C3H, and WRKY. We also analyzed the expression of genes involved in pathogen-associated molecular pattern (PAMP) recognition, the activation of effector-triggered immunity, TFs, and hormone biosynthesis, as well as genes that are pathogenesis-related, or have roles in signaling/regulatory functions and cell wall modification. Their differential expression patterns were compared among mock-/inoculated- and resistant/susceptible cotton. Our results suggest that the cotton defense response has significant transcriptional complexity and that large accumulations of defense-related transcripts may contribute to V. dahliae resistance in cotton. Therefore, these data provide a resource for cotton improvement through molecular breeding approaches. CONCLUSIONS: This study generated a substantial amount of cotton transcript sequences that are related to defense responses against V. dahliae. These genomics resources and knowledge of important related genes contribute to our understanding of host-pathogen interactions and the defense mechanisms utilized by G. barbadense, a non-model plant system. These tools can be applied in establishing a modern breeding program that uses marker-assisted selections and oligonucleotide arrays to identify candidate genes that can be linked to valuable agronomic traits in cotton, including disease resistance.

Coupling interactions between sulfurous acid and the hydroperoxyl radical.

Radical-molecule complexes associated with the hydroperoxyl radical (HOO) play an important role in atmospheric chemistry. Herein, the nature of the coupling interactions between sulfurous acid (H(2)SO(3)) and the HOO radical is systematically investigated at the B3LYP/6-311++G(3df,3pd) level of theory in combination with the atoms in molecules (AIM) theory, the natural bond orbital (NBO) method, and energy decomposition analyses (EDA). Eight stable stationary points possessing double H-bonding features were located on the H(2)SO(3)...HOO potential energy surface. The largest binding energies of -12.27 and -11.72 kcal mol(-1) are observed for the two most stable complexes, where both of them possess strong double intermolecular H-bonds of partially covalence. Moreover, the characteristics of the IR spectra for the two most stable complexes are discussed to provide some help for their possible experimental identification.

[AFLP analysis of cotton with fusarium and verticillium wilts from the Huanghe and Changjiang valleys].

Genetic diversity among 101 cottons varieties, including 72 cultivars from the Huanghe valley and 29 cultivars from the Changjiang valley, was investigated using AFLP markers. In total, 20 primer combinations revealed 200 polymorphic bands among the Huanghe valley cottons and 127 polymorphic bands among the Changjiang valley, respectively. Euclidean distance values were calculated using SPSS (11.0) software. Average Euclidean distance value was 4.356 (the Huanghe valley) and 4.391 (the Changjiang valley), respectively. When the value was 15.2, 72 varieties from the Huanghe valley were divided into four groups (the Huanghe valley groups, abbrevate HVGs), including HVG1 (27), HVG2 (19), HVG3 (10) and HVG4 (16). 29 varieties from the Changjiang valley were classified into four groups (the Changjiang valley groups, abbreviate CVGs), including CVG1 (14), CVG2 (4), CVG3 (5) and CVG4 (6). Compared with Euclidean distance matrices and frequency distribution of pairwise Euclidean distances of cottons from the Huanghe and Changjiang valleys, it was showed that there was similar genetic diversity between the cotton cultivars from Huanghe valley and those from Changjiang valley.